The invention relates to ultrasonic transducers of the type that do not have to contact the liquid to sense its presence and more particularly to one which can sense the liquid in a vessel or pipe without the need of a coupling compound between the transducer and the vessel or pipe.
Transducers for transmitting and receiving ultrasonic energy in applications involving liquids are well known. A typical application for such transducers is in liquid level sensing to sense the height of a liquid in a container or other vessel, such as a tank. Another application is in flow meters where the rate of flow in a pipe is measured. The most widely used form of such transducer has a housing that contains a piezo-electric element. The housing is mounted to the vessel or pipe with the front end of the housing extending trough a hole placed to be in direct contact with the liquid. The ultrasonic energy is coupled directly to the liquid to sense its presence or the energy dissipates in air when no liquid is present.
Another type of ultrasonic transducer is of the non-contact type, such as disclosed in U.S. Pat. No. 4,630,245, granted Dec. 16, 1986. Here, the transducer housing is of a rigid material, such as a plastic, and is fixedly mounted, such as by a clamp or strap, to the outside of the vessel or pipe in which the liquid being sensed is present. While the non-contact type transducer has an advantage in that no hole has to be made in the vessel or pipe to which it is mounted, it requires a coupling compound, such as Vaseline, or silicon grease, between the housing and the vessel or pipe. The coupling compound is needed so that there will be no air gaps between the transducer housing and the vessel or pipe since this would adversely affect the transmission and reception of the ultrasonic energy from the transducer to the wall of the vessel or pipe and thereafter to the liquid or air therein.
Application of the coupling compound in the foregoing type of non-contact transducer is another step required in the mounting of the transducer. Also, the need for using a coupling compound also limits the use of such a transducer, for example, in an application for sensing the liquid level in bottles moving rapidly past a fixed inspection point on an assembly line. Here, it would not be possible to apply the coupling compound to each of the bottles. Also, in some applications, the use of a coupling compound can adversely affect the appearance of the pipe or vessel. Further, in sensitive sanitary applications such as drug and food processing, the use of such coupling compound should or must be avoided. Another disadvantage in this type of non-contact transducer is that it is fixed in position and cannot be easily moved. Accordingly, a need exists for a non-contact type ultrasonic transducer that is not subject to these limitations.
In accordance with the invention, a non-contacting type ultrasonic transducer is provided having a housing in which the piezo-electric element is mounted in contact with a sealed capsule of a membrane of a flexible material. The capsule contains a material, such as a liquid or grease, capable of transmitting ultrasonic energy. A part of the flexible membrane of the capsule, which can be dome shaped, extends out of the front of the transducer housing and makes contact with the article, such as a vessel, pipe, or container or other member, that contains the liquid to be sensed. The capsule front end is pressed against the article and deforms to thereby make a good coupling with the article wall. Ultrasonic energy is transmitted from the piezo-electric element through the capsule membrane in the transducer housing, the liquid in the capsule liquid and the portion of the capsule that extends from the housing to the wall of the article and the liquid, or absence of liquid, contained therein that is being sensed. When there is liquid in the article at the level of contact of the transducer membrane, the path is reversed on the return trip of the ultrasonic energy through the capsule and its liquid to the piezo-electric element. When no liquid is present in the article, the energy dissipates and there is no return energy to be received by the piezo-electric element.
The transducer of the invention can be operated by and used with a variety of conventional ultrasonic devices, such as used for measuring liquid level, liquid flow rate or other similar application and applications requiring a momentary contact such as sensing the liquid level in bottles or cans moving past an inspection station in an assembly line. The use of the deformable capsule does not require any coupling compound. Therefore, no time or effort is required to apply the coupling compound and no residue of a compound is left on the wall of the article. Since the transducer does not have to be fixedly mounted to the article, it can be used in a portable manner.
It is an object of the invention to provide an ultrasonic transducer of the non-contact type.
A further object is to provide a non-contacting type ultrasonic transducer for sensing the presence or absence of liquid in an article in which no coupling compound is required between the transducer housing and the article wall.
Yet another object is to provide a non-contacting type ultrasonic transducer having a deformable member that contacts the wall of the article containing liquid being sensed to couple ultrasonic energy to and from liquid contained in the article.